sorry but it isn’t very clear because if, for example, you try to edit a 10GB file
you would immediately get a response that this won’t work and it is very unlikely
that there will be a solution in the near future.
BUT if you try to edit a 100MB file the answers would be different with some additional questions.

sorry but scintilla has, afaik, a 2 GB limit.
But this doesn’t mean that you can open a 2 GB file as scintilla internally
needs to allocate more bytes depending which lexer is used and if folding is active
and …
In addition the limit happens also if you have multiple big files you want to open
and which might have a total of 2 GB.

I don’t know that it is a “problem” to not be able to open a 3GB file in Notepad++…well, maybe except for you. Notepad++, as others have stated, doesn’t have opening files that large in its design criterion.